In recent years, there are increasing cases where a touch panel system which receives an instruction from a user by detecting a position of an indicator (for example, a finger of the user, a stylus pen, or the like; the same shall apply hereinafter) which is in contact with or proximate to a detection surface of a touch panel is mounted to an electronic information apparatus such as a cellular phone or a personal computer. Particularly, there are increasing cases where a capacitive touch panel of a projection type, which allows multi-touch, is mounted to an electronic information apparatus.
In such a touch panel system, the indicator which is in contact with or proximate to the detection surface is detected based on a processing result of a signal generated by the touch panel. However, the signal generated by the touch panel is affected by various influences such as stain adhering to the detection surface and aging degradation in addition to non-uniformity of a structure of the touch panel. Accordingly, in a case where the indicator is detected by directly using the processing result of the signal generated by the touch panel, sensitivity of the detection surface for detecting an indicator becomes non-uniform.
When the detection sensitivity of the detection surface for detecting the indicator becomes non-uniform in this manner, it may happen that it is easy to detect an indicator at a certain position in the detection surface while it is difficult to detect the indicator at a different position in the detection surface, for example.
Then, it is considered that calibration (correction) is executed based on the processing result of the signal generated by the touch panel in a state where there is no indicator which is in contact with or proximate to the detection surface (hereinafter, referred to as “non-indicated state”). When the calibration is executed, variations of the detection sensitivity due to the above-described various influences are suppressed in a processing result of a signal generated by the touch panel, which is to be obtained thereafter. Thus, it becomes possible to make the detection sensitivity of the detection surface for detecting an indicator more uniform.
Since distribution of electrostatic capacitance of the touch panel changes due to a change in temperature, a change with time, and the like, it is preferable that the calibration be regularly performed not only at a time of manufacture but also at a time of turning on the power or the like.
However, a calibration is not always executed in the non-indicated state. For example, when the calibration is executed in a state where the indicator is in contact with or proximate to a certain position in the detection surface, in subsequent processing, an influence of the indicator which is in contact with or proximate to the detection surface is suppressed at this certain position. Accordingly, in the certain position, the detection sensitivity of the detection surface for indicating an indicator becomes significantly deteriorated and, in some cases, it is not allowed to detect the indicator.
In PTL 1, described is that, in a case where a human sensor senses presence of an approaching object during automatic calibration, the automatic calibration of a touch panel is stopped. Incorrect calibration is thereby prevented from being performed.